Syllabus Edition

First teaching 2023

First exams 2025

|

Nucleic Acids (HL IB Biology)

Exam Questions

2 hours37 questions
1a2 marks

Describe the main role of DNA. 

1b2 marks

The image below shows a representation of several nucleotides in a molecule of DNA.

e-1b

Identify the structures marked Y and Z.

1c2 marks

Identify the nitrogenous bases in part b) marked X and W.

1d1 mark

DNA and RNA are referred to as polynucleotides.

State the meaning of the prefix 'poly' in the term polynucleotide

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2a
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2 marks

In a section of DNA 17 % of the nucleotides were found to contain cytosine.

Calculate the percentage of thymine in this section of DNA. 

2b1 mark

State one reason why the calculation from part a) could not be performed for a piece of RNA. 

2c3 marks

The diagram below shows a representation of part of a DNA molecule.

diagram-5_letters

Identify the structures labelled A, B, and D.

2d1 mark

Identify one type of bond found within the structure labelled C in the diagram at part c).

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3a4 marks

One mark is available for clarity of communication throughout this question.

Draw on and annotate the diagram below to show the correct structure of double-stranded DNA.

bTZZnTVZ_e-5a
3b5 marks

Compare and contrast the structures of DNA and RNA.

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4a
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3 marks

The diagram below represents a nucleosome.

TzZbcTMf_hl-ib-e-7-1-q1a

Label parts A to C on the diagram.

4b
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1 mark

Prokaryotic DNA does not form nucleosomes.

State the reason for this.

4c
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2 marks

In eukaryotes, a great length of DNA is packed into a very small nucleus.

Describe how a nucleosome would contribute to make this possible.

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5a
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1 mark

The diagram below shows the experimental procedure followed by Alfred Hershey and Martha Chase.

jgqFjoK6_hershey-chase

State the aim of this experiment.

5b
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1 mark

Based on the information in the diagram at part a), state one reason why viruses were used in this experiment.

5c
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2 marks

Describe the events taking place between step 1 and 2 of the experiment.

5d
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2 marks

State the results obtained at the end of step 3.

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6a
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4 marks

One mark is available for clarity of communication throughout this question.

Describe the roles of non-coding regions of DNA molecules.

6b
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5 marks

Molecular visualisation software is a useful tool with which to study the structure of molecules.

State five applications of molecular visualisation software in the fields of medicine and science.

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1a1 mark

The 3D shape of DNA is know as a double helix. 

State whether it is possible for a strand of RNA to form a double helix. 

1b1 mark

State how the two strands of the DNA molecule held together.

1c1 mark

State the part of a DNA molecule that contains nitrogen.

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2a2 marks

Using appropriate shapes to represent chemical structures, draw and label a single RNA nucleotide.

2b2 marks

A section of DNA was found to contain the following percentages of bases, as shown in the table below.

  %
  Adenine Cytosine Guanine Thymine
Sense strand 15     27
Antisense strand   23    


Use your knowledge of DNA structure to complete the table by filling in the missing boxes.

2c3 marks

The diagram below shows DNA replication.

biology-2-5-sq-ib-hl-q2c

Identify the enzyme shown in the diagram and describe its function.

2d1 mark

Indicate with a tick or ticks () in the table below the chemical group(s) that appear(s) at the two ends of a single strand of DNA.
 

  Deoxyribose sugar Phosphate
3' (3-prime) end    
5' (5-prime) end    

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3a1 mark

The diagram below shows a base pair within a molecule of DNA.

biology-2-5-q3a-sq-ib-hl-med

Identify part P of this section of DNA

3b2 marks

Scientists sequenced the gene for a hormone, in order to understand more about why some individuals stop producing this hormone. The scientists determined that the gene consisted of 1 500 base pairs; 30% of the total bases were cytosine.

How many nucleotides of adenine and guanine were there in this sample of DNA?        

3c3 marks

Describe the conventional numbering system for carbon atoms in a pentose sugar such as the ribose or deoxyribose sugars found in RNA and DNA. You may sketch a diagram to illustrate your answer.

3d
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2 marks

Many visualisation techniques have been used to understand and study the structure of DNA. James Watson and Francis Crick used visualisation techniques, such as Rosalind Franklin’s X-ray diffraction, to build a physical model of DNA. Their models were also influenced by the findings of other researchers, such as Erwin Chargaff.

Describe how the research findings of Chargaff facilitated Watson, Crick and Franklin to determine the structure of DNA.

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4a2 marks

The diagram below shows the process of DNA replication. The horizontal lines represent the positions of bases.

biology-2-5-q4a-ib-hl-med

Identify the parts of the DNA molecule represented by the labels W, X, Y and Z.

4b2 marks

The table shows the percentage of different bases in the DNA of some organisms.

Organism Percentage of each base
Adenine Guanine Cytosine Thymine
Human 32.8 17.2 17.2 32.8
Caterpillar 33.1 16.9 16.9 33.1
Mouse    22.4    
Virus 24.7 24.1 18.5 32.7


Calculate the missing figures for mouse DNA and complete the table.

4c3 marks

Humans and caterpillars have very similar percentages of each base in their DNA but are not the same class of organism.

Use your knowledge of DNA structure and function to explain how this is possible.

4d2 marks

The DNA of the virus is different from that of the human, caterpillar and mouse. Some viruses contain single-stranded DNA that is not base-paired to a complementary strand. Use data from the table in question 4b) to show evidence for this difference.

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5a2 marks

Some DNA is associated with a protein called histone, which packages the DNA into structures called nucleosomes.

Describe the structure of a nucleosome. 

5b2 marks

State the functions of nucleosomes.

5c2 marks

Within the nucleus, DNA is replicated semi-conservatively in order to produce new cells. 

State two features of DNA and explain how these features are important in the process of semi-conservative replication of a cell’s DNA.

5d3 marks

The diagram below shows DNA replication.

q1d_7-1_dna_structure_replication_medium_ib_hl_biology_sq

Name the enzyme shown in the diagram and describe its function.

 

5e3 marks

Today, visualisation software can be utilised to analyse DNA in very high detail. The association between protein and DNA within the nucleosome can be seen.

Describe what may be visualised when analysing a nucleosome.

5f3 marks

The diagram below shows DNA replication.

q1d_7-1_dna_structure_replication_medium_ib_hl_biology_sq

Name the enzyme shown in the diagram and describe its function.

 

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1a3 marks

The ends of a DNA strand are referred to as the 3’ end and the 5’ end.

Describe the aspects of DNA structure that give rise to this naming system.

1b2 marks

Adenine/thymine and guanine/cytosine form hydrogen-bonds with each other in complementary base-pairing within the DNA double helix. These bases can also form bonds with other molecules in order to carry out their function.

(i)

Suggest one other molecule that might form bonds with the bases in a DNA molecule.

[1]

(ii)

State the role of the molecule identified in part i).

[1]

1c4 marks

The structure of DNA has many characteristics that enable it to carry out its function.  

(i)

Identify two structural features that help DNA to carry out its function.

[2]

(ii)

For each feature identified at part i), explain how it assists with DNA function.

[2]

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2a
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2 marks

Even the smallest DNA molecules are very long.

  • A kilobase (Kb) is a unit equivalent to 1000 base pairs of a DNA molecule.
  • One Kb of double stranded DNA has a length of 0.34 μm.

The DNA in the nucleus of a cell from a fruit fly (Drosophila) is 5.6 cm long.

Calculate the number of Kb in the DNA of the fruit fly. Give your answer to the nearest whole number.

2b1 mark

The amount of DNA found in the nucleus of cells can vary amongst people, with each human chromosome containing between 5 x 104 and 26 x 104 Kb of DNA.

Suggest one reason why people might have different quantities of DNA to each other.

2c1 mark

Other than for use in replication, explain one advantage of DNA molecules having two strands.

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3a
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4 marks

A section of DNA contains 1,200 base pairs.

  • The number of guanine molecules on strand one was counted as 156.
  • The number of cytosine molecules on strand one was counted as 209.
  • The number of adenine molecules on strand two was counted as 264.

Complete the table below to include the total number of each base present in the section, and the % composition of each base. 

  Number of molecules present % composition
Adenine    
Cytosine    
Guanine    
Thymine    

3b2 marks

The image below shows a section of the skeletal formula of a DNA molecule.

Number the carbon atoms of all the pentose sugars shown in the image using the standard numbering format.

h-4b

3c2 marks

The DNA nucleotides are covalently bonded together in the sugar-phosphate backbone between the pentose sugar and the phosphate group, however, they are hydrogen bonded together between the bases. 

Explain why both types of bonds are important for the functioning of DNA. 

3d1 mark

During DNA replication both DNA strands act as a template, whereas in transcription only one strand acts as a template. 

Outline what is meant by the word 'template' in this context. 

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4a4 marks

ATP is a source of energy used in cells and is produced from processes such as respiration. 

The structure of ATP is shown in the diagram below.T7rO3wHK_h-5a

Use the information in the diagram, as well as your own knowledge, to compare and contrast the structure of ATP with an adenine DNA nucleotide.

4b4 marks

Explain how the structure of DNA allows replication.

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5a
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2 marks

Arginine is an amino acid found in histone proteins and plays an important role in the interaction between histones and DNA within nucleosomes.

The diagram below shows the structure of arginine and a section of DNA within a nucleosome.

arginine-dna-bond-in-nucleosome-sqarginine-dna-bond-in-nucleosome-sq

Suggest how arginine facilitates the interaction between histones and DNA, by using the information in the diagram.

5b
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2 marks

Explain the role of nucleosomes in chromosome structure.

5c
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2 marks

Packing ratio is determined by dividing the length of DNA packed into a structure by the length of the structure.

Chromosome 11 consists of about 1.35 x 108 base pairs and the distance between adjacent base pairs is 3.4 nm. The chromosome is about 5 µm in length during metaphase.

Calculate the packing ratio of chromosome 11. Show your working.

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6a
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2 marks

The following table shows the DNA base composition of different organisms. Note that for E. coli, the %C and %T has deliberately been left out.

Organism %A %C %T %G
Maize 26.7 23.3 27.0 23.0
Chicken 28.0 21.9 27.8 22.3
Octopus 33.0 17.2 32.1 17.7
Grasshopper 29.8 20.2 29.2 20.8
Sea urchin 32.6 16.9 33.1 17.4
Yeast 31.5 18.1 32.1 18.3
E. coli 24.7 - - X

State two deductions that can be made from the data.

6b
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2 marks

Calculate the possible value of X in the table in part a).

Show your working.

6c
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2 marks

The results from part a) are similar to those first obtained by Erwin Chargaff in the 1950s. 

Suggest how Chargaff's research may have impacted the work of Crick and Watson.

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